There has been generally used a cylindrical punch blade by which a plastic film is punched so that an aperture should be formed in the plastic film. For example, Japanese Patent Publication No. 35,318 of 1992 discloses a cylindrical punch blade moved toward a plastic film and a die to be pressed against the plastic film, the plastic film being sandwiched between the punch blade and the die. The plastic film is therefore punched by the punch blade and the die so that an aperture should be formed in the plastic film. The patent publication further discloses that the punch blade is moved toward the plastic film and a receiver to be pressed against the plastic film, the plastic film being sandwiched between the punch blade and the receiver. The punch blade is rotated by a drive to make the plastic film punched.
In addition, there exists a problem that the plastic film generates a waste when being punched. The waste may be caught in the punch blade. In this connection, in the apparatus of the patent publication, the punch blade includes a spring and a pin received therein so that the waste should be removed by the spring and the pin after the plastic film is punched.
On the other hand, for example, in a machine for successively making plastic bags of plastic film, it may be required to make a number of apertures formed in the plastic film so that the plastic bag should include the apertures formed therein for venting. In this case, in order to make the apertures formed in the plastic film by utilizing the apparatus of the patent publication, not only the punch blades but also the dies or the drives for rotation have to be disposed in the positions of apertures, to be high in cost.
In addition, the apertures have to be formed in the plastic bag to be small in diameter for venting. In this connection, it is difficult to make the spring and the pin received in the punch blade. The punch blade can therefore include no spring and pin by which the waste is removed, resulting in the problem of the waste being caught in the punch blade.
By the way, Japanese Patent No. 3,655,627 discloses a machine for successively making plastic bags in which plastic films are fed longitudinally thereof and intermittently. The plastic films are heat sealed with each other and cross cut by a heat seal device and a cutter when the plastic films are stopped temporarily whenever being fed intermittently, to successively make the plastic bags. The same is true of the punch blade. The plastic film is punched by the punch blade when the plastic films are stopped temporarily whenever being fed intermittently.
It is therefore an object of the invention to provide a plastic film punching apparatus improved to prevent the waste from being caught in the punch blade, without involving the problem of cost.